Coil form

ABSTRACT

A coil form which includes an internal threadably movable core and in the coil there are a plurality of longitudinally extending rigid ribs which are cut by the advancing threaded core forming grooves and in which there are longitudinally extending flexible or rubbery rib means which engage the core and to resist rotation so that a predetermined tune is maintained with the rubbery material resisting rotation of the core while the rigid ribs resist withdrawal or movement of the core in response to direct axial force.

United States Patent McFarlane Sept. 9, 1975 [54] COIL FORM 3,011,138 11/1961 Andalek 336 136 x 3,105,948 10/1963 McFarlane 336 136 [76] Inventor: Rl?hard McFarlane, 40 589 3,281,744 10/1966 Melanson 336 136 x Oaks Charles, 3,355,533 11/1967 Mistic 336/136 x 60174 3,453,163 7/1969 Nlills et a1. 336 136 x [22] Filed: May 21, 1974 3,458,844 7/1969 Hildebrandt 336/136 x 1 1 Appl- NO-I 472,065 Primary ExaminerThomas J. Kozma Related US. Application Data [63] Continuation of Ser. No. 343,661, March 22, 1974,

abandoned.

[52] US. Cl. 336/136 [51] Int. Cl. HOIF 21/06 [58] Field of Search 336/130, 136, 198

[56] References Cited UNITED STATES PATENTS 2,462,822 2/1949 WOOd 336/136 2,584,723 2/1952 Macker 336/136 2,838,738 6/1958 Andalek et a1. 336/136 2,995,719 8/1961 Osborn et a1. 336/136 [57] ABSTRACT A coil form which includes an internal threadably movable core and in the coil there are a plurality of longitudinally extending rigid ribs which are cut by the advancing threaded core forming grooves and in which there are longitudinally extending flexible or rubbery rib means which engage the core and to resist rotation so that a predetermined tune is maintained with the rubbery material resisting rotation of the core while the rigid ribs resist withdrawal or movement of the core in response to direct axial force.

8 Claims, 7 Drawing Figures COIL FORM This is a continuation of application Ser. No. 343,661, filed Mar. 22, 1974, now abandoned.

BACKGROUND OF THE INVENTION Coil forms are employed widely in the electronics industry; and the difficulty of maintaining critical or sensistive coil tuning, i.e., the precise axial positioning of a threaded core in a coil form, is a recognized problem in the art. I

To secure a core in a coil against axial forces tending to displace it, it has been known in the past to provide a tubular coil form having internal, longitudinally extending, relatively rigid ribs to be threadably engaged by a threaded core, the dore being self-threading as it is advanced by cutting into the rigs. The rigid ribs serve to resist withdrawal or advancement from a predetermined set position in response to axial forces exerted on the core. However, in transit or for many varied reasons, the core may be inadvertently rotatably moved which axially displaces the core slightly, oftentimes a sufficient amount so that a sensitive adjustment is lost. This occurs in part because the rigid ribs, once cut by the advancement of a threaded core, define a track which is characterized by relatively low resistance to turning. The present invention provides, in addition to the rigid ribs, a plurality of flexible ribs of rubbery material extending axially, preferably between the rigid ribs, which increases the torque and, therefore resists rotation of the core upon accidental threaded advancement or withdrawal of the core so that it does not become easily displaced.

Another problem in the art is that threaded adjustment of a core in a coil form having rigid ribs is that the rotation tends to be abrupt as opposed to smooth. The flexible, rubbery ribs of the present invention provide a smoothness to turning forces on the core, making it easier to set the core at a critical predetermined location.

OBJECTS OF THE INVENTION It is accordingly an object of this invention to provide an improved coil form with a threadably movable core within the coil, which coil is characterized by a tubular core housing having longitudinally extending rigid ribs and longitudinally extending flexible rubbery rib means for (a) increased torque resistance, and (b) control in adjustment of the core.

It is a general object of this invention to provide a coil form in which the core is not susceptible to displacement by rotation of it, except by intentional rotation, which would otherwise detune the same, and which includes longitudinally extending flexible rib means in addition to or in lieu of conventional rigid ribs to provide increased resistance to movement of the core by torque within the coil so as not to be affected by, for example, vibration or movement.

It is the particular object of this invention to provide an improved coil form embodiment which includes a tube of circular cross section including three equispaced longitudinally extending rigid ribs and three intermediate equally spaced flexible, rubbery, longitudinally extending ribs, the flexible ribs being approximately midway between the longitudinal rigid ribs, the same being a preferred embodiment while under certain conditions it may be preferable to increase or decrease the number of rigid and flexible ribs.

In accordance with the foregoing objects, the instant invention will now be described with reference to the accompanying drawings in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a coil form constructed according to our preferred embodiment of the instant invention;

FIG. 2 is a view in cross section taken on the plane indicated by the line 2-2 of FIG. 1 and looking in the direction of the arrows;

FIG. 3 is a view in cross section taken on the plane indicated by the line 3-3 of FIG. 2 and looking in the direction of the arrows;

FIG. 4 is an end view of a coil form and illustrating an alternative embodiment of the instant invention;

FIG. 5 is an end view of a second alternative embodiment of the instant invention;

FIG. 6 is a view in cross section taken on the plane indicated by the line 66 of FIG. 5 and looking in the direction of the arrows; and

FIG. 7 is a view in cross section of a final alternative embodiment of the instant invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION A preferred embodiment of the improved coil form includes (a) a tube 10 of rigid circular cross section with (l) a plurality of circumferentially spaced axially or longitudinally extending, inwardly protruding ribs of relatively rigid material designated by the numeral 14, and, (2) between each of the relatively rigid ribs, a longitudinally extending relatively resilient or flexible rib of rubbery material, designated by the numeral 16, and (b) a threaded core 18 within the tube and in threaded engagement with the ribs. The rigid ribs resist axial forces tending to displace the core and the flexible ribs resist threaded advancement or retraction of the core to maintain the core in a preset or tuned condition.

Generally, each coil form or tube is sized to accept a threaded tuning core 18 which is sized to mate with it, the core being commercially available generally of material selected from the class that includes iron, ferrite, brass, aluminum, steel or other suitable material. The coil form is designed such that the threads of the tuning core do not contact the interior wall 20 of the tube but, rather the threads bite into the terminal end of the longitudinally extending rigid ribs so that, as the core is threadably advanced, the threads cut thread grooves on the rigid ribs. Preferably, the tuned end zone of the longitudinally extending rigid ribs are relatively fine and the engagement of the core is not deep so as to have a small resistive effect to the turning force, that is the torque required to threadably move the tuning core axially relative to the coil form, while at the same time the rigid ribs by their engagement with the threads of the core provide resistance to axial displacement of the core within the tube in response to any axially directed pushing or pulling force on the core. The terminal ends of the flexible rubbery ribs 16 are more displaced than cut by the threads of the tuning core when it is threadably advanced or retracted and account for substantially most of the turning force required to thread the tuning core into and out of the tube, once the rigid rib thread grooves have been cut by an initial advancement of the core into the form.

As an example, a tuning'core having a 0.249 thread diameter may be utilized with a coil form having an outside diameter of approximately 0.297 and an inside diameter of 0.254 a clearance of approximately 0.0025 to 0.003 between the tuning core and the interior surface of the rigid circular wall of the tube. The longitudinal internal rigid ribs are approximately 0.004 wide and the effective inside diameter measured across a circle defined by the terminal ends of these ribs is approximately 0.243, which allows the tuning core to cut a thread into these ribs to a depth of approximately 0.003, which provides effective resistance to axial forces applied to the core while causing little resistance when threading the core into the form. The heighth and width of the alternately spaced longitudinally resilient ribs is generally dependent upon the durometer, or resistance, of the material used for these ribs. The softer the material used the higher and/or wider the rib must be to provide an adequate torque level or resistance to turning and the less resilient the material the smaller the rib size is required to be to produce the same torque level. Materials the hardness of which is about a Shore A durometer range of approximately 30 to 100 are preferred. When the material is approximately 70 Shore A durometer range, the rib width should be approximately 3/64th wide and the effective inside diameter measured over these ribs should be approximately 0.235, which allows an engagement between the core thread and the longitudinal resilient ribs of approximately 0.007. The threads of the tuning core do not cut into but, rather, displace the rib to produce friction on threaded movement of the core, i.e., the torque level. The most common size of this type of coil form accommodate cores with a range of 0.112 to 0.305 outside thread diameter with the outside diameter of the form running in the range of 0.160 to 0.353 respectively.

The coil form and rigid ribs may be molded or extruded of either thermo-setting or thermo-plastic material in the relatively rigid range with the internal flexible or rubbery ribs being molded or extruded into the form simultaneously. Alternatively, the tube and internal rigid ribs may be extruded or molded and, thereafter, the internal resilient ribs are applied in a secondary operation. Typical material for the flexible internal ribs in an acceptable hardness range are selected from the class which includes polyurethane, flexible polyester, flexible epoxy, silicone rubber and various other rubbery materials, including flexible poly vinyl chloride.

In this manner a coil form is produced which provides good mechanical strength and accurate torque control. Once set, the setting of the internal tuning core in the coil form of the preferred embodiment in relation to an external winding is positive and resists axial displacement as by axial forces as well as slight turning on movement or vibration of a unit on which the coil form has been installed, so that a sensitive adjustment which has been made will be maintained.

DESCRIPTION OF ALTERNATIVE EMBODIMENTS While in the preferred embodiment described above the relatively flexible or rubbery ribs are alternately spaced so that one is between each of the relatively rigid ribs, this arrangement is not necessarily required. As seen in FIG. 4, at least one flexible rib means 16,

which may be a single rubbery rib, provides resistance to displacement by rotation of the core 18. An additional alternative embodiment is set forth in FIGS. 5 and 6, in which all or some of the end zones of the rigid ribs may be coated with rubbery material; and in such an embodiment the core is sized such that the outside diameter of the threads bites into the rigid material of the rib a short distance and displaces the flexible rib so that a portion of the rubbery material is captivated between adjacent teeth of the core and the root of the thread of the core.

With respect to this latter embodiment of FIGS. 5 and 6, it is seen in reference to the drawings that the diameter of the core 30 relative to the inside diameter of the tube wall-32 is such that the rib of rigid material 34 is grooved by the terminal ends of the threads 36 and the rubbery material 38 on the terminal end of the rib 34 is displaced and captivated between the adjacent teeth, such as 36 and 40 so that the rubbery material resists rotation by engaging the thread roots.

In a final alternative embodiment, see FIG. 7, a relatively rigid tubular length comprises the coil form 10 and the ribs 16 are each of rubbery material and engage the threads of the core 18.

What is claimed is:

l. A coil form including a tubular length of circular cross section and of relatively rigid material, including a plurality of relatively rigid internal ribs projecting a substantially common radial distance into the column of the length, a threaded core within the length of a diameter less than the inside diameter of the tubular length and of a diameter greater than the diameter of a circle through the terminal ends of the ribs for threaded advancement or retraction of the core within the length and to resist axial displacement by axial forces on the core, and longitudinally extending flexible rib means in the column of the tubular length in engagement with the core and providing resistance to turning of the core to maintain a predetermined position of the core in the length.

2. The coil form as set forth in claim 1 wherein the rib means comprise a plurality of longitudinally extending ribs.

3. The coil form as set forth in claim 2 wherein the flexible ribs and the rigid ribs are spaced alternately about the column of the length.

4. The coil form as set forth in claim 3 wherein the spacing between the ribs is about 60.

5. The coil form as set forth in claim 4 wherein three of the ribs are of relatively rigid material and three of the ribs are of said flexible material.

6. The coil form as set forth in claim 1 wherein the flexible ribs are of rubbery material selected from the class of materials having a Shore A durometer range of between 30 and 100.

7. The coil form as set forth in claim 1 wherein the rib means are characterized by a durometer of approximately Shore A.

8. A tubular length of relatively rigid material having a plurality of radial ribs circumferentially spaced and extending axially substantially the length of said tube, said ribs comprising a pattern of interdigitated hard and soft ribs, said hard ribs being adapted to resist axial withdrawal of a threaded torque threadably engaged interiorly in the column of said tube and said soft ribs being adapted to provide frictional resistance to resist torque forces caused by joggling of a unit in which the coil is mounted and resists rotation out of adjustment of said torque within said coil. 

1. A coil form including a tubular length of circular cross section and of relatively rigid material, including a plurality of relatively rigid internal ribs projecting a substantially common radial distance into the column of the length, a threaded core within the length of a diameter less than the inside diameter of the tubular length and of a diameter greater than the diameter of a circle through the terminal ends of the ribs for threaded advancement or retraction of the core within the length and to resist axial displacement by axial forces on the core, and longitudinally extending flexible rib means in the column of the tubular length in engagement with the core and providing resistance to turning of the core to maintain a predetermined position of the core in the length.
 2. The coil form as set forth in claim 1 wherein the rib means comprise a plurality of longitudinally extending ribs.
 3. The coil form as set forth in claim 2 wherein the flexible ribs and the rigid ribs are spaced alternately about the column of the length.
 4. The coil form as set forth in claim 3 wherein the spacing between the ribs is about 60*.
 5. The coil form as set forth in claim 4 wherein three of the ribs are of relatively rigid material and three of the ribs are of said flexible material.
 6. The coil form as set forth in claim 1 wherein the flexible ribs are of rubbery material selected from the class of materials having a Shore A durometer range of between 30 and
 100. 7. The coil form as set forth in claim 1 wherein the rib means are characterized by a durometer of approximately 70 Shore A.
 8. A tubular length of relatively rigid material having a plurality of radial ribs circumferentially spaced and extending axially substantially the length of said tube, said ribs comprising a pattern of interdigitated hard and soft ribs, said hard ribs being adapted to resist axial withdrawal of a threaded torque threadably engaged interiorly in the column of said tube and said soft ribs being adapted to provide frictional resistance to resist torque forces caused by joggling of a unit in which the coil is mounted and resists rotation out of adjustment of said torque within said coil. 